INSIDER VIEW 1948: Mitropoulos rehearsing James Aliferis No 1

Pretty unique find in the archive - a rehearsal of Dimitri Mitropoulos working the Minneapolis Symphony through a challenging modern piece by James Aliferis (Symphony #1) on March 19th, 1948.
Aliferis was a student in 1941, with Leonard Bernstein and Lukas Foss, in Serge Koussevitsky's first conducting class at the Berkshire Music Center. I can find little else about Aliferis or this symphony so if you know more please comment!
The unique thing about this is you can hear Mitropoulos’ distinct voice as he starts and stops the orchestra through various sections. At one point early on you can hear him singing the violin lines along with them. He famously didn’t work with scores and had an incredible memory. I’m pretty sure he’s humming along at a different point in the rehersal.
The first part of the recording is not very high quality - mostly because the tape was very old, on an acetate backing which had hardened and peeled away some of the oxide. But the later half of the recording is of stellar quality. The brass section in particular is electrifying.
At the end of the recording you hear that this was a broadcast of KUOM, the University of Minnesota radio station. Based on the quality of this recording and previous notes from Reynolds Marchant, I believe this was recorded directly off the line at Northrup Auditorium that fed the radio broadcast.
Technical info:
Unknown Scotch, maybe 102
7” Reel
7 1/2 IPS
00:00 - Aliferis Symphony #1 rehearsal
12:42 - KUOM Announcer